The present invention relates to sliding gate valves for controlling the flow of molten metal from teeming vessels. Such valves normally comprise a pair of refractory plates arranged to be slidable with respect to one another and containing through-openings that coact to control the flow of metal passing through the valve in accordance with the degree of registration therebetween.
It is incumbant in the operation of valves of the sliding gate type that an accurate amount of sealing pressure be applied between the plates. The application of excessive sealing pressure between the plates impedes, or may even prevent, relative sliding movement therebetween thus rendering the valve inoperative. The application of too little pressure, on the other hand, can result in metal leakage between the plates.
Sealing pressure is generally applied between the plates in such valves by imparting an upward bias against the slide plate forcing it into fluid tight sliding contact with the mating top plate positioned thereabove. Although, as shown in U.S. Pat. No. 3,511,261 granted May 12, 1970 to Bick, et al, this upward bias may be applied by accurately torquing the threaded connectors that maintain the valve components in assembled relation, more desirably the bias is provided by the application of spring pressure which, as shown in U.S. Pat. No. 4,063,668 granted Dec. 20, 1977 to E. P. Shapland, et al, may take the form of an array of mechanical springs set in the gate frame below the gate plate and arranged about the metal flow opening to apply an upward bias around the opening effective to place the mating surfaces of the plates in fluid tight sliding contact.
Locating the springs in close proximity to the plate opening through which molten metal flows has the undesirable effect of subjecting them to the elevated temperatures produced by the molten stream. The springs are accordingly subjected to thermal stresses which can result in relaxation and ultimate failure of the springs unless adequate cooling thereof is provided as, for example, by the application of a cooling air flow thereto.
It has been suggested, in order to ameliorate the aforementioned problem, to provide a sliding gate valve mechanism in which the springs for applying seal pressure between the refractory plates are located in a position remote from the plates and, concomitantly, from the metal flow stream, and to impart the spring bias to the plates through an appropriate elongated and articulated connecting linkage. Such a valve arrangement is shown and described in U.S. Pat. No. 3,937,372 granted Feb. 10, 1976 to C. H. Bode, Jr. Use of the valve described in this patent under adverse metal pouring conditions indicates that the arrangement is not totally dispositive of the problem however due in part to the fact that the springs may yet undergo relaxation and the elongated linkage is itself subjected to heat and thereby prone to elongate whereupon the effective seal pressure is reduced.
It is to the solution of the aforementioned problems, therefore, that the present invention is directed.